1. Field of the Invention
The present invention relates to a two-way clutch for use in a power transmission mechanism, an auxiliary driving system and the like of an automobile, and transmits and cuts off rotational torque in two directions of a normal rotation direction and a reverse rotation direction.
2. Description of the Related Art
In general, a two-way clutch is used as a unit that switches the transmission path for power in a power transmission mechanism, an auxiliary driving system and the like of an automobile. For example, when a hybrid vehicle having two power sources that are an internal combustion engine and an electric motor travels by the electric motor in addition to the internal combustion engine, the rotation of the electric motor is transmitted to the output shaft via a two-way clutch in both normal and reverse rotation directions. Further, as described in Japanese Patent Application Laid-Open No. 2002-5200, two-way clutches are also adopted in an auxiliary drive system using an electric motor in combination, a center differential of a four-wheel vehicle and the like.
In the two-way clutch in Japanese Patent Application Laid-Open No. 2002-5200 described above, a cylindrical surface is formed in any one of an inner race and an outer race, while a cam surface is formed in the other one of the inner race and the outer race, and rollers as torque transmission members are interposed between the cylindrical surface and the cam surface. The two-way clutch adopts the structure that retains the rollers in the neutral position or one of the engaging positions by a spring or a leaf spring, and switches the phase of the cage that retains the torque transmission member by an electromagnetic clutch mechanism or a friction drive mechanism.
However, the two-way clutch in which the torque transmission member is retained in the neutral position of the cam surface has the structure in which the torque transmission member is retained by an urging unit provided in the cage, and therefore, has the problem that the torque transmission member cannot be reliably retained in the neutral position. In the two-way clutch in which the torque transmission member is retained in one of the engaging positions of the cam surface, the cylindrical surface and the torque transmission member slide in contact with each other, and therefore, there is the problem that drag torque (dragging torque) occurs at a non-operation time of the two-way clutch (idling time) and reduction in fuel efficiency and the like due to the drag torque occurs.